I'm just getting back into backpacking from a time before silnylon, so I don't have any silnylon gear yet.
One of the Walmarts in my area still has a fabric section and I found some dark green ripstop nylon in their bargain remnants. It feels pretty slick, and both sides look/feel the same. I don't think that I was able to blow air through it. I stretched some of it over a large mixing bowl, and poured a couple cups of water into it, which it held overnight.
This all sound like what I've read about silnylon, however, the cut edges do fray, which I've read shouldn't happen with sil. Are there any tests that I can do to make sure that it's silnylon before I go back and buy a bunch more of it?